1. Field of the Invention
The present invention relates to a Stirling engine, and in more detail, relates to a heater for a Stirling engine which enables further improvement in heat exchange efficiency.
2. Description of the Prior Art
Generally speaking, a Stirling engine is aimed at realizing Stirling's cycle, which is formed by the four processes of an isothermal compression 1.fwdarw.2, an isochoric cooling 2.fwdarw.3, an isothermal compression 3.fwdarw.4, and an isochoric heating 4.fwdarw.1, as shown in FIG. 1. As one Stirling engine for realizing the Stirling's cycle, there is known a two-piston type engine which is shown in FIG. 2. It has a first cylinder 14 and a second cylinder 16 with a first power piston 10 and a second power piston, respectively, that have a phase difference of about 90.degree. between them. The first cylinder 14 and the second cylinder 16 are connected through three heat exchangers, namely, a heater 18, a regenerator 20, and a cooler 22 within the first cylinder 14 and the second cylinder 16, there is sealed a fixed amount of working fluid which is heated or cooled by the heater 18 or the cooler 22. The operation of the above Stirling engine can be described as follows. After self-sustaining operation of the engine is realized, in the isochoric heating period, the first power piston 10 moves downward from the top dead point, with accompanying heated expansion (the pressure going up) of the expansion space. At the same time, the second power piston 12 moves upward toward the top dead point. Therefore, the volume of the working fluid remains unchanged, with a shift of the working fluid at lower temperature toward the higher temperature side, in which the working fluid is heated to a higher temperature by recovering heat from the regenerator. Since, in the isothermal expansion period, the first power piston 10 moves further downward and the second power piston 12 comes down also, the space for the working fluid expands and its pressure goes down. During this period, the Stirling engine transfers energy to the exterior due to the heating by the heater. In the isochoric cooling period, the first power piston 10 moves upward from the bottom dead point and the second power piston 12 moves to the bottom dead point, so that the volume of the working gas at a higher temperature shifts toward the lower temperature side, with its temperature being reduced by storing heat in the regenerator 20. In the isothermal compression period, the first power piston 10 moves further upward and the second power piston 12 moves upward also, so that the space for the working fluid is compressed with the accompanying rise in the pressure. During this period, the Stirling engine receives energy from the exterior.
The difference between the energy output to the exterior during the isothermal expansion and the energy received from the exterior during the isochoric compression becomes the net output of the Stirling engine, the magnitude of which is proportional to the difference between the temperatures of the expansion and the compression and to the amount of the gas stored in the engine. The regenerator 20 is for storing the heat during the isochoric cooling with the temperature difference being maintained as well, and for utilizing the heat by regenerating it during the isochoric heating, which enables one to attain a more satisfactory heat efficiency.
In the prior art Stirling engine of two-piston type, one end of a cooler 25, which extends approximately perpendicularly in the direction of action of the second power piston, is joined to the upper portion of a second cylinder 24, and the other end of the cooler 25 is joined to one end of a regenerator 28, as shown by FIG. 3. The other end of the regenerator 28 and the upper portion of a first cylinder 26 are connected with a plurality of heating pipes 30, and a combustion chamber 34 is formed by providing a combustion duct 32 around the heating pipes 30. It is arranged to heat the working fluid in the heating pipes 30 by burning the combustion gas which is introduced through the combustion gas intake 35 provided on the combustion duct 32. However, in the prior art Stirling engine of the above kind, the duct lengths of the working fluid between the first cylinder 26 and the regenerator 28 become unequal because of the nonuniformity in the length of the plurality of heating pipes 30 due to structural reasons. Accordingly, the flow amount of the higher temperature fluid in the heated state that is in each of the heating pipes 30 becomes nonuniform. In addition, in the Stirling engine as described above, where the heating parts in the combustion chamber 34, namely, the heating pipes 30, are expanded by heating, there will be applied an excessive force to each of the joining sections, adversely affecting a cause, for reading in the life of the device. This leads to a reductin in the output performance of the engine as a result of reduction in the heat input, restrained by the heating pipes with smaller amount of flow, of the temperature of the combustion gas that heats the heating pipes. Furthermore, the distribution of the combustion gas becomes nonuniform, preventing improvement in the heat exchange efficiency.